I. Field of the Invention
The present invention relates generally to devices and methods for attaching soft tissue to bone, and more particularly to devices for anchoring sutures into the bone so that soft tissue can be attached thereto.
II. Description of Prior Art
In the field of orthopedic surgery, there are occasions when a ligament must be reattached to bone. For example, the ligaments surrounding the shoulder, elbow or knee may become detached from the bone due to a traumatic injury. Repair of these types of damages and restoration of the function of the ligament depends heavily on the extent to which the ligament is allowed to grow back into the bone from which it has become separated. In view of the difference in density between the tissues involved, conventional suturing of the ligament to the bone must often be augmented by the use of anchoring devices which are forcibly inserted into the bone. These anchoring devices, which are capable of holding a desired length of suture thread, are generally constructed of a biocompatible metal or possibly an absorbable material. Depending upon the type of anchor employed, the suture is either attached to the anchor prior to insertion, or it may be attached after the anchor is implanted into the bone. In either case, once the suture and anchor are in place, the suture extending from the anchor is then used to tie the ligament against the bone in a manner which allows the ligament to grow into the bone mass.
One such device and method for suture attachment is disclosed in U.S. Pat. No. 5,156,616 issued to Meadows and Ogden (hereinafter "Ogden"), the disclosure of which is incorporated herein by reference. The device comprises a cannulated bone screw constructed of a biocompatible metal, wherein the body includes exterior screw threads for inserting and retaining the screw into bone. A passageway extends completely through the body of the screw, where the passageway is divided into a central portion and a distal portion. The central portion and distal portion of the passageway are both large enough to accommodate the size of suture threads. However, the distal portion is larger than the central portion in order to accept a suture thread knot. Thus, the relative sizes of the central portion and the distal portion are such that the suture thread knot can be held within the distal portion, but prevented from passing through the central portion. Opposite from the distal portion, the screw also includes means for cooperating with an external drive tool to drive the screw into the bone, such as a hexagon- or square-shaped socket. The driving tool is also cannulated or slotted, which protects the suture threads extending from the proximal portion from being damaged during insertion. As an alternative, a longitudinal groove may be formed into the side of the socket adjacent to the path of the tool to achieve the same purpose.
In operation of the Ogden anchor, suture thread is passed through the passageway so that a part of the suture extends beyond the distal portion of the screw. The excess suture is tied into a knot and then pulled through the passageway until the knot becomes seated within the distal portion and abuts the central portion of the passageway. The screw is then placed into the bone after the formation of a suitable pilot hole.
While the Ogden anchor does appear to provide favorable results, it fails to provide "bidirectional" anchoring. As used herein, the term "bidirectional" means the capability of a cannulated screw to safely accommodate suture threads extending from either (or both) the distal or (and) proximal portion of the screw. Specifically, the anchored sutures in Ogden may only extend from the proximal portion of the screw, because the suture knot must be contained within the distal portion of the passageway. In the existing design for the Ogden anchor, as seen in FIGS. 2, 5, and 6 of that reference, there are no structural features which can safely accommodate a proximal knot and distally extending suture threads. Although there is a cavity present at the proximal end of the Ogden anchor, it is intended exclusively for receiving an external driving tool to insert the screw into the bone. Thus, the drive socket is not designed to accept a suture thread knot.
For example, a suture knot placed into the Ogden drive socket (prior to the modifications disclosed herein) would create at least two detrimental effects. First, the presence of any obstruction in the drive socket (such as a knot) would hinder the insertion of the anchor into the bone, because there would be less contact between the socket and the driving tool. This condition can result in misalignment of the anchor, and it can cause damage to surrounding tissue if the tool should slip from the socket during insertion. Second, the pressure of the metal driving tool is often quite high as the self-tapping screw threads of the anchor are urged into the cancellous bone. If a suture knot were pinched between the drive socket and the tool, the suture threads may be damaged or completely severed, thus jeopardizing the critical tensile strength of the threads.
The same limitations seen in the Ogden anchor can also be found in certain bone fixation screws. For example, in the bone fixation screw manufactured by Acumed, Inc., and marketed under the trade name "Acutrak", a headless compression screw with variable pitch threads is used to join fractured bone fragments. This device is also cannulated to allow its insertion over a guide pin. although it lacks the ability to receive suture threads as explained by Ogden. While the Acutrak device is well-suited to rejoining cancellous bone, its utility would be greatly enhanced if an Ogden-type suture anchoring feature were implemented. Moreover, modification of the Acutrak device to include "bidirectional" suture anchoring would undoubtedly increase its advantages in bone fixation applications.
Therefore, the present invention builds upon the utility of the Ogden anchor and the Acutrak bone fixation screw by the combined use of a distal recess at the insertion end of either device, as well as a proximal recess formed below the drive socket. The proximal recess in both cases would be similar in size and shape to the distal recess described in the Ogden reference, and it would permit the placement of suture thread extending from the distal end of either screw. Moreover, as the central passageway may be sized to accommodate multiple threads, the invention is quite advantageous in situations which may require sutures extending from both ends of the anchor or fixation screw, as the case may be. This simple, yet critically important, modification to the foregoing prior art devices safely allows their use in a wider variety of surgical procedures, as will be explained in greater detail below.